Production of multilayer photographic materials



N. R. WVYNN 2,941,898

PRODUCTION OF MULTILAYER PHOTOGRAPHIC MATERIALS June 21, 1960 Filed Nov. 24, 1958 PRODUCTION OF'MULTILAYER PHOTOGRAPHIC MATERIALS Norman Ratclitfe Wynn, Ilford, England, assignor to llford Limited, Ilford, England, a British company Filed NOV. 24, 1958, Ser. No. 776,013

Claims priority, application Great Britain Dec. 16, 1957 5 Claims. (Cl. 117-34) This invention relates to the processes and apparatus for the production of multilayer photographic materials.

Whilst photographic film consists essentially only of a light-sensitive layer on a support, it is customary to include other layers, e.g. a so-called subbing layer, which serves to increase the anchorage between the film and the light-sensitive layer, and a so-called supercoat layer which serves to protect the light-sensitive layer from mechanical damage. Moreover, it is frequently the case that more than one light-sensitive layer is necessary, and this is particularly the case in respect of materials for colour photography which commonly have at least three light-sensitive layers, usually with inter-layers or filter layers.

It is thus commonly demanded in the manufacture of photographic materials that a multiplicity of layers should be coated in superposition on a single support. Customarily the layers (which most commonly have a basis of gelatin) are coated in succession with each layer being set, and possibly dried, before the next is applied. Attempts have been made to coat a multiplicity of layers without the intervening'setting (and possibly drying), but there is then a serious difficulty in maintaining the layers entirely distinct from one another sinceeach layer after the first is being coated on the wet surface of the last applied layer.

Because of this difficulty attention has been directed to other methods of achieving the coating of several superimposed layers, and one such method proposedis to arrange that the materials for the successive layers are applied by a coating method in which the materials are in laminar flow in a bead between the outlet of a hopper and the surface of a travelling film base.

It is an object of the present invention to provide a method of satisfactory multiple coating without intermixing of the successive layers, in'which the layers are applied separately but in close succession.

According to the present invention 'a process for coating a plurality of layers on a web support in the production of a photographic material comprises applying a plurality of coating liquids to the travelling support from ite States l atertt stations spaced at short distances apart, whereby'the web support picks up coating liquid from each of said stations in succession, the coating solutions after the first thus being applied to a liquid layer derived from-the next preceding coating station, each of the'said liquidsafter that first applied being metered to the support through a slot extending across theweb and constituting at its coating station a bead of coating liquid connecting the said slot and the surface being coated. If desired the first applied solution may also be meteredthrough a slot to form a bead as aforesaid.

The invention further includes apparatus for carrying out the process as aforesaid.

The method of coating just referred to isnot to be confused with extrusion coating. in extrustion coating the liquid is extruded through the slot as a ribbon which 2341898 Patented June-21, 196i) is laid as such on the surface to be coated. ln therproc ess of the present invention it is essential that the liquid leaving the slot in metered amount should establish a bead of liquid from which liquid is-continuously withdrawn by the travelling web. It will generally be found that the bead so orients itself that one or both of the lips of the slot are wholly within the bead. I

It is found that by the aforesaid method of coating successive layers can be applied which, despite the fact that liquid coatings are being applied on to liquid layers applied from the preceding coating stations, do not intermingle but maintain their laminar integrity.

It is advantageous to arrange that the support being coated travels round an upper quadrant of a horizontal drum, the coating stations being located in succession adjacent that upper quadrant so that the first coating is applied while the support is travelling in agenerally upward direction and the later coatings at positions where the support is travelling in a successively more horizontal direction. In this way it is arranged that as the applied coatings become more'numerous, and therefore in total more substantial, the tendency to run-back due to gravity is reduced.

The present invention further includes apparatus for carrying out the process defined above comprising-means for causing a web support to move in a predetermined path and a plurality of coating devices each adapted to apply a liquid layer to the said web and located at-stations spaced short distances apart along the said path, each said coating device comprising a chamber having a slot therein extending across the width of the web, and means for metering coating liquid to said chamber to cause said liquid to issue through said slot, the said slot being located relative to the path of travel of the web so that liquid issuing from said slot on to the web in said path establishes and maintains a bead of said liquid between said slot and said web.

The invention will now be further described with reference to the accompanying drawings in which:

Figure 1 diagrammatically illustrates a form of coating apparatus according to the invention.

Figure 2 diagrammatically illustrates a portion of Figure 1 on an enlarged scale.

Figure 3 illustrates in diagrammatic section a single coating unit as employed in the apparatus of Figures 1 and 2.

Referring to Figure 1, photographic film base 1 is fed from a supply (not shown) over a roller and round a drum 2 rotating in the direction of the arrow. Successive coatings are applied at the coating stations 3, 4 and 5, and the coated film passes off the drum to drying apparatus, or through a chill box and then a drying apparatus (these elements are not characteristics of the present invention and are therefore not shown).

In Figure 2 the three coating heads 3, 4 and 5 are shown in greater detail, the applied coating liquids being shown in shading.

In Figure 3 there is shown in cross section the coating head 4. It is shown with the film base 1 carrying a first liquid coating 6 approaching the head 4 and leaving with a second liquid coating 7 superimposed on the coating 6.

The coating head 4 (which is similar in construction to the coating heads 3 and 5) consists of a chamber 8 including a jacket 9 through which liquid at con-trolled temperature may be circulated. The entry port of the liquid is shown at 10; the exit port is not shown on this diagram; but can be located at any convenient point. Bolted to the chamber 8' by bolts 11 is a coating member 12 having a slot 13 connecting the bottom of the member 12 to an inner chamber 14. Coating liquid 17 supplied via port 15 charges the inner chamber 14 and passes out through the slot 13 to lay a coating 7 on the liquid coated film 1, 6 passing beneath it. As indicated, a bead 16 of the liquid 17 is formed between the jaws of the slot 13 and the liquid-coated film 1, 6. It will be appreciated that the coating head 4 extends across the width of the film to be coated, i.e. the slot extends across thatwhole width.

The coating liquid 17 is metered to the chamber 14 by any convenient means (not shown), e.g. by means of a gear pump.

For optimum results care must be given to the design of the coating member 12 and in particular to the shape of the jaws of the slot 13. In the coating of photographic emulsions of the normal range of viscosities the slot width may vary, for example from to 60 thousandths of an inch. In general the slot width should be as great as can conveniently be used since in this way the system becomes less sensitive to slight inaccuracies in the dimensions of the slot. Moreover, the danger of the slot becoming clogged is reduced.

The inner face 18 of the slot may be, for example, to inch in length. Excessively short lengths tend to increase danger of damage to the jaws of the slot, while excessively great lengths create a condition of viscous drag which may act up inaccuracies of coating.

The bottom faces 19 of the slot should be as large as convenient because in general if these faces are large it permits larger slot widths to be used and the jaws are also more robust. Generally they may be, for example, it; to inch in width. However, the upper practical limit is set, when the coating is being applied on a curved surface, as in the example illustrated, by the curvature of the surface adjacent the slot.

The gap between the slot and the surface being coated, which is bridged by the bead 16, may vary according to the other conditions. In general a gap of 5 to 60 thousandths of an inch is suitable, the preference being for larger gaps since with these, inaccuracies of the thickness of the support being coated, inaccuracies in the setting of the roller 2 and inaccuracies in the contour of that roller tend to be of less importance, and there is further a lesser danger of the gap becoming clogged.

Apart from the foregoing dimensional conditions it is important, if the best results are to be obtained, that the coating member 12 should not itself introduce coating defects by reason of its having a non-smooth surface; all corners should be rounded and the whole of the surfaces should be highly polished. In this way a streamlined smooth flow may be maintained in the bead.

Further, in the preferred form of the invention the coating heads in a series have slots of increasing length across the width of the film being coated. In this way undesirable edge effects which sometimes arise when the coatings are of equal width can be avoided.

Although the apparatus has been illustrated to show the coatings being applied in a generally downward direction, this is not essential and the coating heads can be provided so that the coating is applied in a horizontal or generally upward direction. Moreover, although in the illustration given the coatings are applied to film passing round a drum, this is not a necessary-feature of the invention since the coatings may be applied to film passing in a plane at any angle.

The coating method of the invention permits of applying to film base'thinner coating layers than can be applied by conventional methods of coating. Moreover, by the method of the invention, whereby a liquid layer is coated on to a liquid layer already present, it is possible to achieve very much thinner coatings, for example coatings as little as $6 of the thickness of those applied by conventional methods.

What I claim is:

1. A process for coating a plurality of layers, on a web support in the production of a photographic material which comprises applying a plurality of coating liquids to the travelling support from stations spaced at short distances apart, whereby the web support picks up coating liquid from each of said stations in succession, the coating solutions after the first thus being applied to a liquid layer derived from the next preceding coating station, each of the said liquids after that first applied being metered to the support through a slot extending across the web and constituting at its coating station a bead of coating liquid connecting the said slot and the surface being coated.

2. A process for coating a plurality of layers on a web support in the production of a photographic material which comprises applying a plurality of coating liquids to the travelling support from stations spaced at short distances apart, whereby the web support picks up coating liquid from each of said stations in succession, the coating solutions after the first thus being applied to a liquid layer derived from the next preceding coating station, each of the said liquids being metered'to the support through a slot extending across the Web and constituting at its coating station a bead of coating liquid connecting the said slot and the surface being coated. 3. Apparatus for coating a plurality of layers on a web support comprising means for causing a web support to move in a predetermined path and a plurality of coating devices each adapted to apply a liquid layer to the said web and located at stations spaced short distances apart along the said path, each said coating device comprising a chamber having a slot therein extending across the width of the web, and means for metering coating liquid to said chamber to cause said liquid to issue through said slot, each said slot being located relative to the path of travel of the web so that liquid issuing from said slot on to the web in said path establishes and maintains a head of said liquid between said slot and said Web.

4. Apparatus for coating a plurality of layers on a web support comprising a drum around which the web is caused to pass in a path thus predetermined by the contour of said drum, and a plurality of coating devices each adapted to apply a liquid layer to the said web and located at stations spaced short distances apart along the said path, each said coating device comprising a chamber having a slot therein extending across the width of the web, and means for metering coating liquid to said chamber to cause said liquid to issue through said slot, each said slot being located relative to the path of travel of the web so that liquid issuing from said slot on to the web in said path establishes and maintains a bead of said liquid between said slot and said web.

5. Apparatus for coating a plurality of layers on a web support comprising a drum around which the web is caused to pass in a path thus predetermined by the contour of said drum, and a plurality of coating devices each adapted to apply a liquid layer to the said web and located at stations spaced short distances apart along the said path, each said coating device comprising a chamber having a slot therein extending across the width of the web, and means for metering coating liquid to said chamher to cause said liquid to issue through said slot, each said slot being located relative to the path of travel of the web at an upper rising gradient of the circumference of the drum so that liquid issuing from said slot on to the web in said path establishes and maintains a bead of said liquid between said slot and said web.

References Cited in the file of this patent UNITED STATES PATENTS 2,681,294 Beguin June 15, 1954 2,761,417 Russell et al. Sept. 4, 1956 2,761,419 Mercier et al. Sept. 4, 1956 2,761,791 A Russell Sept. 4, i956 

1. A PROCESS FOR COATING A PLURALITY OF LAYERS ON A WEB SUPPORT IN THE PRODUCTION OF A PHOTOGRAPHIC MATERIAL WHICH COMPRISES APPLYING A PLURALITY OF COATING LIQUIDS TO THE TRAVELLING SUPPORT FROM STATIONS SPACED AT SHORT DISTANCES APART, WHEREBY THE WEB SUPPORT PICKS UP COATING LIQUID FROM EACH OF SAID STATIONS IN SUCCESSION, THE COATING SOLUTIONS AFTER THE FIRST THUS BEING APPLIED TO A LIQUID LAYER DERIVED FROM THE NEXT PRECEDING COATING STATION, EACH OF THE SAID LIQUIDS AFTER THAT FIRST APPLIED BEING METERED TO THE SUPPORT THROUGH A SLOT EXTENDING ACROSS THE WEB AND CONSTITUTING AT ITS COATING STATION A BEAD OF COATING LIQUID CONNECTING THE SAID SLOT AND THE SURFACE BEING COATED. 